Recent years have seen a rapid expansion in the performance of solid state lighting devices such as light emitting devices (LEDs); and with improved performance, there has been an attendant expansion in the variety of applications for such devices. For example, rapid improvements in semiconductors and related manufacturing technologies are driving a trend in the lighting industry toward the use of light emitting diodes (LEDs) or other solid state light sources to produce light for general lighting applications to meet the need for more efficient lighting technologies and to address ever increasing costs of energy along with concerns about global warming due to consumption of fossil fuels to generate energy. LED solutions also are more environmentally friendly than competing technologies, such as compact fluorescent lamps, for replacements for traditional incandescent lamps.
The actual solid state light sources, however, produce light of specific limited spectral characteristics. To obtain white light of a desired characteristic and/or other desirable light colors, one approach uses sources that produce light of two or more different colors or wavelengths and one or more optical processing elements to combine or mix the light of the various wavelengths to produce the desired characteristic in the output light. In recent years, techniques have also been developed to shift or enhance the characteristics of light generated by solid state sources using phosphors, including for generating white light using LEDs. Phosphor based techniques for generating white light from LEDs, currently favored by LED manufacturers, include UV or Blue LED pumped phosphors. In addition to traditional phosphors, semiconductor nanophosphors have been used more recently. The phosphor materials may be provided as part of the LED package (on or in close proximity to the actual semiconductor chip), or the phosphor materials may be provided remotely (e.g. on or in association with a macro optical processing element such as a diffuser or reflector outside the LED package). The remote phosphor based solutions have advantages, for example, in that the color characteristics of the fixture output are more repeatable, whereas solutions using sets of different color LEDs and/or lighting fixtures with the phosphors inside the LED packages tend to vary somewhat in light output color from fixture to fixture, due to differences in the light output properties of different sets of LEDs (due to lax manufacturing tolerances of the LEDs).
Hence, solid state lighting technologies have advanced considerably in recent years, and such advances have encompassed any number of actual LED based lamp products as well as a variety of additional proposals for LED based lamps. However, there is still room for further improvement in the context of solid state lamp products that are compatible with existing standardized light sockets and therefore might be adopted as replacements for conventional incandescent lamps, compact fluorescent lamps, or other similar older technology lamps.
For example, there is always a need for techniques to still further improve efficiency of solid state lamps, to reduce energy consumption. Also, any new solution should provide a light output distribution that generally conforms to that of the standard lamp it may replace, so as to provide a light output of color, intensity and distribution that meets or exceeds expectations arising from the older replaced technologies. As another example of a desirable characteristic for a solid state lamp, for general lighting applications, it is desirable to consistently provide light outputs of acceptable characteristics (e.g. white light of a desired color rendering index and/or color temperature) in a consistent repeatable manner from one instance of a lamp product to another.
Of course, to be commercially competitive with alternative lamp technologies requires an elegant overall solution. For example, the product should be as simple as possible so as to allow relatively low cost manufacturing. Relatively acceptable/pleasing form factors similar to those of well accepted incandescent lamps may be desirable. Solid state devices have advantages of relatively high dependability and long life. However, within the desired lamp form factor/configuration, there are a variety of technical issues relating to use of solid state devices that still must be met, such as efficient electrical drive of the solid state light emitters, efficient processing of the light for the desired output and/or adequate dissipation of the heat that the solid state devices generate.